Electronic devices often contain displays. A display may have an active area with pixels that display images for a user and an inactive area alongside the active area. A layer of glass may serve as a protective display cover layer. The layer of glass may overlap the active area and the inactive area. To hide internal components from view, the inner surface of the inactive area may be covered with an opaque masking layer such as a layer of black ink. Windows in the display cover layer may be formed from openings in the opaque masking layer. Light-sensitive components may be aligned with the windows. For example, an ambient light sensor may be aligned with a window in a display.
To improve the outward appearance of the display cover layer in the inactive area, ambient light sensor windows may be covered with coatings of dark ink. Dark ink coatings for ambient light sensor windows are sometimes referred to as ambient light sensor inks. The presence of the ambient light sensor ink on an ambient light sensor will darken the outward appearance of the ambient light sensor window and thereby help visually blend the ambient light sensor window with surrounding portions of the layer of black ink in the inactive area. At the same time, the ambient light sensor ink will be sufficiently transparent to allow ambient light to reach the ambient light sensor that is aligned with the ambient light sensor window.
Although the presence of ambient light sensor ink on an ambient light sensor window may help improve device aesthetics, the presence of the ambient light sensor ink may introduce non-ideal characteristics to an ambient light sensor system. For example, ambient light sensor readings may vary as a function of the angle of incidence of incoming ambient light with respect to the ambient light sensor system.